RandomGenerator.h

/*
 *  Phusion Passenger - http://www.modrails.com/
 *  Copyright (c) 2010 Phusion
 *
 *  "Phusion Passenger" is a trademark of Hongli Lai & Ninh Bui.
 *
 *  Permission is hereby granted, free of charge, to any person obtaining a copy
 *  of this software and associated documentation files (the "Software"), to deal
 *  in the Software without restriction, including without limitation the rights
 *  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 *  copies of the Software, and to permit persons to whom the Software is
 *  furnished to do so, subject to the following conditions:
 *
 *  The above copyright notice and this permission notice shall be included in
 *  all copies or substantial portions of the Software.
 *
 *  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 *  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 *  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 *  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 *  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 *  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 *  THE SOFTWARE.
 */
#ifndef _PASSENGER_RANDOM_GENERATOR_H_
#define _PASSENGER_RANDOM_GENERATOR_H_

#include <string>

#include <boost/noncopyable.hpp>
#include <boost/shared_ptr.hpp>
#include <oxt/system_calls.hpp>

#include "StaticString.h"
#include "Utils.h"
#include "Exceptions.h"


/**
 * A random 
 */
namespace Passenger {

using namespace std;
using namespace boost;
using namespace oxt;

/**
 * A random data generator. Data is generated using /dev/urandom, and
 * is cryptographically secure. Unlike rand() and friends,
 * RandomGenerator does not require seeding.
 *
 * The reason why RandomGenerator isn't a singleton is because opening
 * /dev/urandom is *very* slow on Mac OS X and OpenBSD. Each object of
 * this class caches the /dev/urandom file handle.
 *
 * This class is thread-safe as long as there are no concurrent
 * calls to reopen() or close().
 */
class RandomGenerator: public boost::noncopyable {
private:
        FILE *handle;
        
public:
        RandomGenerator(bool open = true) {
                handle = NULL;
                if (open) {
                        reopen();
                }
        }
        
        ~RandomGenerator() {
                this_thread::disable_syscall_interruption dsi;
                close();
        }
        
        void reopen() {
                close();
                handle = syscalls::fopen("/dev/urandom", "r");
                if (handle == NULL) {
                        throw FileSystemException("Cannot open /dev/urandom",
                                errno, "/dev/urandom");
                }
        }
        
        void close() {
                if (handle != NULL) {
                        syscalls::fclose(handle);
                        handle = NULL;
                }
        }
        
        StaticString generateBytes(void *buf, unsigned int size) {
                size_t ret = syscalls::fread(buf, 1, size, handle);
                if (ret != size) {
                        throw IOException("Cannot read sufficient data from /dev/urandom");
                }
                return StaticString((const char *) buf, size);
        }
        
        string generateByteString(unsigned int size) {
                char buf[size];
                generateBytes(buf, size);
                return string(buf, size);
        }
        
        string generateHexString(unsigned int size) {
                char buf[size];
                generateBytes(buf, size);
                return toHex(StaticString(buf, size));
        }
        
        /**
         * Generates a random string of <em>size</em> bytes which is also
         * valid ASCII. The result consists only of the characters A-Z,
         * a-z and 0-9, and therefore the total number of possibilities
         * given a size of N is 62**N. However not every character has an
         * equal chance of being chosen: a-i have 5/256 chance of being
         * chosen, while other characters have 4/256 chance of being chosen.
         * Therefore, to match the entropy of a random binary string of
         * size N, one should choose a <em>size</em> which yields slightly
         * more possibilities than 2**N.
         */
        string generateAsciiString(unsigned int size) {
                static const char chars[] = {
                        'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm',
                        'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z',
                        'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M',
                        'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z',
                        '0', '1', '2', '3', '4', '5', '6', '7', '8', '9'
                };
                unsigned char buf[size];
                generateBytes(buf, size);
                for (unsigned int i = 0; i < size; i++) {
                        buf[i] = chars[buf[i] % sizeof(chars)];
                }
                return string((const char *) buf, size);
        }
        
        int generateInt() {
                int ret;
                generateBytes(&ret, sizeof(ret));
                return ret;
        }
        
        unsigned int generateUint() {
                return (unsigned int) generateInt();
        }
};

typedef shared_ptr<RandomGenerator> RandomGeneratorPtr;

} // namespace Passenger

#endif /* _PASSENGER_RANDOM_GENERATOR_H_ */

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